1. Field of the Invention
The present invention relates to a photoelectrochemical cell, and more particularly, to a dye-sensitized solar cell. The present invention also relates to a particulate structure, a semiconductor electrode for a dye-sensitized solar cell, an electrolyte for a dye-sensitized solar cell, and a reduction electrode for a dye-sensitized solar cell.
2. Description of the Related Art
A photoelectrochemical cell is collectively referred to a cell that, upon receiving light, an electrochemical reaction occurs and an electric potential difference between both electrodes is generated. The types of the photoelectrochemical cells generally include a photovoltaic cell and a photoelectrolytic cell.
The representative example of the photovoltaic cell type of the photoelectrochemical cell is a dye-sensitized solar cell. The dye-sensitized solar cell was first developed by Michael Gratzel and colleagues at EPFL (Ecole Polytechnique Federale de Lausanne) in Switzerland in 1991 (see U.S. Pat. Nos. 5,350,644, 5,441,827 and 5,728,487). The dye-sensitized solar cell is an energy converting apparatus that converts light energy into electrical energy. The main constituents of the dye-sensitized solar cell are a photosensitive dye that absorbs the visible light and generates electron-hole pairs, and a transition metal oxide semiconductor that transfers the generated electrons. The dye-sensitized solar cell can be used as a sensor or a power supply.
The production cost of the dye-sensitized solar cell is low and the efficiency of the energy conversion is high compared with a silicon photocell using a pn junction of a semiconductor. The dye-sensitized solar cell is a promising device that can serve as a substitute for the silicon photocell which has high production costs.
The operating principle of the general dye-sensitized solar cell is illustrated in FIG. 1. As illustrated in FIG. 1, when a ray of light, such as solar light is irradiated on a semiconductor electrode 11 made up of an n-type metal oxide semiconductor in which dye molecules are chemically adsorbed to its surface, the dye molecules that adsorb the ray of light are electronically raised from the ground state (D+/D) to an excited state (D+/D*) thus generating electron-hole pairs. These electrons (e−) are in the conductive bands of the n-type metal oxide semiconductor. The electrons transferred to the n-type metal oxide semiconductor are transferred to a conductive transparent substrate 12, and then fed to a load L via a conducting wire 13. The electrons passing through the load L are transferred to a platinum reduction electrode 14 via a conducting line 13′.
An oxidation-reduction electrolyte 15 often contains iodide ions and is infused between the semiconductor electrode 11 and the reduction electrode 14. The electronically transited and then oxidized dye molecules (D→D+) receive the electrons provided by the oxidation of iodide ions(3I−1→I3−1) in the oxidation-reduction electrolyte 15, and are reduced again. The oxidized iodide ion receive the electrons from the reduction electrode, and is reduced again.
For the commercialization of such a dye-sensitized solar cell, it is still required to increase the efficiency of the energy conversion. The efficiency of the energy conversion of the dye-sensitized solar cell is influenced by the properties of the metal oxide semiconductor particle, the properties of the semiconductor electrode containing the particle, the properties of the electrolyte, and the properties of the reduction electrode, etc. Accordingly, improvements for these properties are required.